2 unidentified men sought for questioning in Dallas parking garage death of Taylor Gruwell-Miller

Moments later Taylor plummets to her death. Her heartbroken father says his daughter was deliberately pushed over the edge.

"The proudest I was ever of my daughter was when she had my granddaughter. She was a great mother," said Taylor's father Rich Gruwell.

Behind Taylor's laughter, her father Rich admits, his daughter had a dark side.

"Taylor had problems with prescription medications," said Rich Gruwell. "It was a dark time. It was a bad time with Taylor."

But there was new hope for the single mom, who was seeking help at a treatment center.

"She was glad to be there," said Rich. "She became encased in her treatment and she was doing well."

So her father was floored when the facility called to say Taylor has abruptly taken off with another patient.

"She left all her stuff: purse, hair brush, makeup, I.D.," said Rich.

A few hours later Taylor called her dad. He knew in his gut his daughter was in trouble.

"She said 'Hi daddy,' and I said 'Taylor, where are you?' She wouldn't tell me where she was, she just went straight into, 'Daddy, can I have gas money?'" said Rich. "I knew what that meant. She was trying to buy some type of drug. And I said I'm not gonna give you gas money, but wherever you are right now I will come get you, and the conversation ended. That was the last time I heard my daughter's voice, it was at 6:58 p.m., September 21st."

Just two days later Taylor ends up on the third floor of the Ross Apartments parking structure. Police aren't commenting on the case, claiming this is an ongoing investigation. But Rich tells me a man in the video with Taylor is the friend she left with from rehab.

"She definitely didn't know the things that I've since found out [about him]," said Rich. "This isn't a Boy Scout, OK, this isn't someone who's a pillar of our community."

In the video, Taylor and the man are holding hands. But Rich says based on his daughter's body language, he believes she was trying to get away.

"She's pulling away from him, she rolls her head in the air, like 'Oh my God, what are you saying,' or 'Oh my God, what are we doing? I don't want to go,'" said Rich. "That's what it looks like to me."

At about 11 that night they get in the man's black car. That's all the surveillance video cops have released of Taylor so far. But Rich tells Crime Watch Daily that his daughter and her friend drove up to the fifth floor of the parking garage. Moments later he drove back down to the third floor. Taylor was not with him.

Just 20 minutes later, the beautiful young mom is dead.

Taylor was found by a person just walking by and called 911, but Taylor didn't have any identification on her so she was listed by police as an unidentified white female. They had to use her fingerprints to identify her. It took two days to tell her family.

"They [the police] immediately went to see the surveillance videos," said Rich.

What's on the video raises more questions. Taylor's friend reappears on the third floor, shaking hands with a big guy in a white T-shirt. Moments later he's seen walking off with a different guy in a black shirt.

Then the detective tells Rich something he just can't get out of his head: In the part of the surveillance video yet to be released shows one of these guys was on the fifth floor with Taylor and her friend.

"He immediately said 'I don't think this was an accident," said Rich.

Is your daughter's death right now considered a homicide by the police?

"No, not right now," Rich Gruwell tells Crime Watch Daily.

The police report simply says: "unexplained death." But Rich says Taylor's autopsy is very telling.

"The injuries that my daughter sustained to arms and hands and shoulders and the left side of her face was traumatic," said Rich. "When you break both your wrists and arms and some of your shoulder bones, yeah, it would appear that she fell face-first, of trying to stop her fall."

And Rich says something else suspicious is a picture of the ledge Taylor fell over. It's about four feet high. We weren't able to take our cameras into the actual parking garage, but Rich uses another similar wall to demonstrate why he says this was not just a tragic accident. He says anybody tripping and falling would not fall off something that high.

"And it would take someone of pretty good strength to lift someone over that ledge, so that's why I said, I just ruled completely out 'accident,'" said Rich.

And Rich is confident his daughter would never have taken her own life.

"She never once said 'Daddy, I want to kill myself,' 'Daddy, I've got to hurt myself,' 'Daddy, I don't want to live anymore.' She never said that to me," said Rich.

So if Taylor didn't accidentally fall, and she didn't jump, the burning question is: Was she was pushed? Unfortunately police can't find two of the men in the video, and the other one -- the friend last seen with Taylor -- isn't talking. But he did give detectives a written statement.

"He drove my daughter up there with his dog, he let his dog out to play, he left Taylor there, he came back, Taylor was gone," said Rich.

Taylor's dad says there are a lot of problems with the man's statement. One of the most glaring, Rich says: Cops tell him they've seen all of the surveillance video from that night, and they never saw a dog.

"I'm no surveillance video expert but the dog is a pit bull. A pit bull is a very large dog. You show me a pit bull in the video," said Rich. "She opens the car door, he opens the car door, you would thing a dog would go running out. There's no dog."

Now police are asking for your help in identifying the two men seen talking to Taylor's friend. Police want to know what they know about that night.

"There are definitely answers out there," said Rich.

Taylor's dad wants to know why the man last seen with his daughter alive isn't talking.

"I think he's a coward," said Rich. "He was the last person to see my daughter alive, at least one of the last people to see my daughter alive, and you don't respect human life enough to tell anybody what you know.

"Every waking moment of my life right now, I'm thinking about my daughter falling off that building," said Rich Gruwell. "It never leaves my brain. It's gonna be with me for the rest of my life. I think about her two children and how we're gonna tell them about their mother. You owe it to her children to tell the police what happened, if you know of anything. And I believe he knows."